Referring specifically to FIG. 1, the Midrex process is a DR process using a vertical shaft reactor. Iron ore pellets, lump iron ore, or a combination of pellets and lumps are reduced in a vertical shaft or reduction furnace to metallic iron by means of a reducing gas. The reducing gas is produced from a mixture of natural gas and recycled gas from the reduction furnace. The mixture flows through catalyst tubes, where it is chemically converted into a gas containing H2 and carbon monoxide (CO). The desired reducing gas temperature is typically in the range of 900° C. As the iron ore descends through the reduction furnace by gravity flow, the gas ascends through the material column and removes oxygen from the iron carriers. The product DRI is typically 90% to 94% metallic iron. After the DRI exits from the bottom of the vertical shaft reactor, it can be cooled and stored as cold DRI (CDRI), compressed into hot briquetted iron (HBI) and stored, and/or transported as hot DRI (HDRI), for example. A derivative of the Midrex process can use coal through gasification (MXCOL technology) as well.
The process offers the following benefits:                Using natural gas and agglomerated iron ore makes the process simple;        The packed reactor with the counter-current flow of reactants provides high efficiency;        As the doubling of capacity requires only a 40% increase in the reactor diameter, the technology offers good economies of scale; and        The process is highly flexible with regards to iron ore reducing gas sources and plants can operate at a wide spectrum of hydrogen to carbon monoxide ratios (0.5 to 3.5).        
This DRI production process is highly energy efficient, and further energy gains are realized if the HDRI, for example, is immediately transferred to an electric arc furnace (EAF) melt shop or the like. In this manner, the heat from the DR process lowers the cost of melting the DRI in the EAF, significantly cutting energy costs and electrode consumption. The Midrex process represents 70% of the installed DRI capacity worldwide. Other comparable DR processes are also contemplated for use herein.
Currently, numerous operating plants experience the buildup of sintered DRI on the walls of the furnaces used. This buildup can cause the bustle ports to become blocked, preventing gas from properly being distributed through the reduction zone of the furnace. Also, the buildup can suddenly break loose, causing blockages downstream in the furnace discharge. Previous attempts to reduce such buildup came primarily from sizing the ports differently to increase velocity through the ports or changing the refractory design to eliminate any ledges or places for buildup to initiate. These design changes have been largely ineffective, or, at best, it is inconclusive as to whether or not they help to reduce the problem. Thus, what are still needed in the art are methods for reducing the buildup of sintered DRI on the walls of the furnaces used.